feat: Add CryptoAmount and FiatAmount types

This adds a CryptoAmount types that provides a wrapper for the
underlying CryptoAmount object and can provide helpers for converting
from atomic to whole amounts.

This provides a FiatAmount type as well to wrap our fiat amount +
currency pairings in a consistent manner.

lib/coinbase.rb

@@ -13,9 +13,11 @@
 require_relative 'coinbase/constants'
 require_relative 'coinbase/contract_event'
 require_relative 'coinbase/contract_invocation'
+require_relative 'coinbase/crypto_amount'
 require_relative 'coinbase/destination'
 require_relative 'coinbase/errors'
 require_relative 'coinbase/faucet_transaction'
+require_relative 'coinbase/fiat_amount'
 require_relative 'coinbase/middleware'
 require_relative 'coinbase/network'
 require_relative 'coinbase/pagination'

lib/coinbase/crypto_amount.rb

@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+module Coinbase
+  # A representation of a CryptoAmount that includes the amount and asset.
+  class CryptoAmount
+    # Converts a Coinbase::Client::CryptoAmount model to a Coinbase::CryptoAmount
+    # @param amount_model [Coinbase::Client::CryptoAmount] The crypto amount from the API.
+    # @return [CryptoAmount] The converted CryptoAmount object.
+    def self.from_model(amount_model)
+      asset = Coinbase::Asset.from_model(amount_model.asset)
+
+      new(amount: asset.from_atomic_amount(amount_model.amount), asset: asset)
+    end
+
+    # Converts a Coinbase::Client::CryptoAmount model and asset ID to a Coinbase::CryptoAmount
+    # This can be used to specify a non-primary denomination that we want the amount
+    # to be converted to.
+    # @param amount_model [Coinbase::Client::CryptoAmount] The crypto amount from the API.
+    # @param asset_id [Symbol] The Asset ID of the denomination we want returned.
+    # @return [CryptoAmount] The converted CryptoAmount object.
+    def self.from_model_and_asset_id(amount_model, asset_id)
+      asset = Coinbase::Asset.from_model(amount_model.asset, asset_id: asset_id)
+
+      new(
+        amount: asset.from_atomic_amount(amount_model.amount),
+        asset: asset,
+        asset_id: asset_id
+      )
+    end
+
+    # Returns a new CryptoAmount object. Do not use this method.
+    # Instead, use CryptoAmount.from_model or CryptoAmount.from_model_and_asset_id.
+    # @param amount [BigDecimal] The amount of the Asset
+    # @param asset [Coinbase::Asset] The Asset
+    # @param asset_id [Symbol] The Asset ID
+    def initialize(amount:, asset:, asset_id: nil)
+      @amount = amount
+      @asset = asset
+      @asset_id = asset_id || asset.asset_id
+    end
+
+    attr_reader :amount, :asset, :asset_id
+
+    # Returns the amount in atomic units.
+    # @return [BigDecimal] the amount in atomic units
+    def to_atomic_amount
+      asset.to_atomic_amount(amount)
+    end
+
+    # Returns a string representation of the CryptoAmount.
+    # @return [String] a string representation of the CryptoAmount
+    def to_s
+      Coinbase.pretty_print_object(self.class, amount: amount.to_i, asset_id: asset_id)
+    end
+
+    # Same as to_s.
+    # @return [String] a string representation of the CryptoAmount
+    def inspect
+      to_s
+    end
+  end
+end

lib/coinbase/fiat_amount.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module Coinbase
+  # A representation of a FiatAmount that includes the amount and fiat.
+  class FiatAmount
+    # Converts a Coinbase::Client::FiatAmount model to a Coinbase::FiatAmount
+    # @param amount_model [Coinbase::Client::FiatAmount] The crypto amount from the API.
+    # @return [FiatAmount] The converted FiatAmount object.
+    def self.from_model(amount_model)
+      new(amount: amount_model.amount, currency: currency)
+    end
+
+    # Returns a new CryptoAmount object. Do not use this method.
+    # Instead, use CryptoAmount.from_model or CryptoAmount.from_model_and_asset_id.
+    # @param amount [BigDecimal] The amount of the Asset
+    # @param asset [Coinbase::Asset] The Asset
+    # @param asset_id [Symbol] The Asset ID
+    def initialize(amount:, currency:)
+      @amount = BigDecimal(amount)
+      @currency = currency
+    end
+
+    attr_reader :amount, :currency
+
+    # Returns a string representation of the CryptoAmount.
+    # @return [String] a string representation of the CryptoAmount
+    def to_s
+      Coinbase.pretty_print_object(self.class, amount: amount.to_i, currency: currency)
+    end
+
+    # Same as to_s.
+    # @return [String] a string representation of the CryptoAmount
+    def inspect
+      to_s
+    end
+  end
+end

spec/unit/coinbase/crypto_amount_spec.rb

@@ -0,0 +1,163 @@
+# frozen_string_literal: true
+
+describe Coinbase::CryptoAmount do
+  let(:amount) { BigDecimal('123.0') }
+  let(:crypto_amount_model) { instance_double(Coinbase::Client::CryptoAmount, asset: asset, amount: amount) }
+  let(:eth_asset) { build(:asset_model) }
+
+  describe '.from_model' do
+    subject(:crypto_amount) { described_class.from_model(crypto_amount_model) }
+
+    context 'when the asset is :eth' do
+      let(:asset) { eth_asset }
+
+      it 'returns a CryptoAmount object' do
+        expect(crypto_amount).to be_a(described_class)
+      end
+
+      it 'sets the correct amount' do
+        expect(crypto_amount.amount).to eq(amount / BigDecimal(10).power(eth_asset.decimals))
+      end
+
+      it 'sets the correct asset_id' do
+        expect(crypto_amount.asset_id).to eq(:eth)
+      end
+    end
+
+    context 'when the asset is other' do
+      let(:decimals) { 9 }
+      let(:asset) { build(:asset_model, asset_id: 'other', decimals: decimals) }
+
+      it 'returns a CryptoAmount object' do
+        expect(crypto_amount).to be_a(described_class)
+      end
+
+      it 'sets the correct amount' do
+        expect(crypto_amount.amount).to eq(amount / BigDecimal(10).power(decimals))
+      end
+
+      it 'sets the correct asset_id' do
+        expect(crypto_amount.asset_id).to eq(:other)
+      end
+    end
+  end
+
+  describe '.from_model_and_asset_id' do
+    subject(:crypto_amount) { described_class.from_model_and_asset_id(crypto_amount_model, asset_id) }
+
+    context 'when the crypto_amount model asset is :eth' do
+      let(:asset) { eth_asset }
+
+      context 'when the specified asset_id is :eth' do
+        let(:asset_id) { :eth }
+
+        it 'returns a new CryptoAmount object with the correct amount' do
+          expect(crypto_amount.amount).to eq(amount / BigDecimal(10).power(eth_asset.decimals))
+        end
+
+        it 'returns a new CryptoAmount object with the correct asset_id' do
+          expect(crypto_amount.asset_id).to eq(asset_id)
+        end
+      end
+
+      context 'when the specified asset_id is :gwei' do
+        let(:asset_id) { :gwei }
+
+        it 'returns a new CryptoAmount object with the correct amount' do
+          expect(crypto_amount.amount).to eq(amount / BigDecimal(10).power(Coinbase::GWEI_DECIMALS))
+        end
+
+        it 'returns a new CryptoAmount object with the correct asset_id' do
+          expect(crypto_amount.asset_id).to eq(asset_id)
+        end
+      end
+
+      context 'when the specified asset_id is :wei' do
+        let(:asset_id) { :wei }
+
+        it 'returns a new CryptoAmount object with the correct amount' do
+          expect(crypto_amount.amount).to eq(amount)
+        end
+
+        it 'returns a new CryptoAmount object with the correct asset_id' do
+          expect(crypto_amount.asset_id).to eq(asset_id)
+        end
+      end
+
+      context 'when the specified asset_id is another asset type' do
+        let(:asset_id) { :other }
+
+        it 'raise an error' do
+          expect { crypto_amount }.to raise_error(ArgumentError)
+        end
+      end
+    end
+
+    context 'when the asset is not eth' do
+      let(:decimals) { 9 }
+      let(:asset_id) { :other }
+      let(:asset) { build(:asset_model, asset_id: 'other', decimals: decimals) }
+
+      it 'returns a new CryptoAmount object with the correct amount' do
+        expect(crypto_amount.amount).to eq(amount / BigDecimal(10).power(decimals))
+      end
+
+      it 'returns a new CryptoAmount object with the correct asset_id' do
+        expect(crypto_amount.asset_id).to eq(asset_id)
+      end
+
+      context 'when the asset ID does not match the asset' do
+        let(:asset_id) { :different }
+
+        it 'raises an error' do
+          expect { crypto_amount }.to raise_error(ArgumentError)
+        end
+      end
+    end
+  end
+
+  describe '#initialize' do
+    subject(:crypto_amount) { described_class.new(amount: amount, asset: asset) }
+
+    let(:amount) { BigDecimal('123.0') }
+    let(:asset) { Coinbase::Asset.from_model(eth_asset) }
+
+    it 'sets the amount' do
+      expect(crypto_amount.amount).to eq(amount)
+    end
+
+    it 'sets the asset' do
+      expect(crypto_amount.asset).to eq(asset)
+    end
+
+    it "sets the asset_id to the asset's ID" do
+      expect(crypto_amount.asset_id).to eq(:eth)
+    end
+  end
+
+  describe '#to_atomic_amount' do
+    subject(:crypto_amount) { described_class.new(amount: amount, asset: asset) }
+
+    let(:amount) { BigDecimal('123.0') }
+    let(:asset) { Coinbase::Asset.from_model(build(:asset_model, decimals: 3)) }
+
+    it 'returns the amount in atomic units' do
+      expect(crypto_amount.to_atomic_amount).to eq(123_000)
+    end
+  end
+
+  describe '#inspect' do
+    subject(:crypto_amount) { described_class.new(amount: amount, asset: asset) }
+
+    let(:amount) { BigDecimal('123.0') }
+    let(:asset) { Coinbase::Asset.from_model(eth_asset) }
+
+    it 'includes crypto_amount details' do
+      expect(crypto_amount.inspect).to include('123', 'eth')
+    end
+
+    it 'returns the same value as to_s' do
+      expect(crypto_amount.inspect).to eq(crypto_amount.to_s)
+    end
+  end
+end